Clang Flag: -Wignored-attributes / -Wno-ignored-attributes

The Clang compiler flags -Wignored-attributes and -Wno-ignored-attributes control the emission of warnings related to attributes that are ignored because they are not applicable, not supported, or incorrectly used in the given context. Attributes in C and C++ provide additional information to the compiler about the behavior, optimization, and alignment among other aspects of functions, variables, types, and blocks of code. However, not all attributes are applicable everywhere, and some might conflict with others or with certain language features. The -Wignored-attributes flag is part of the -Wattributes group and is responsible for enabling warnings that alert developers when an attribute is being ignored. This could happen for various reasons such as applying an attribute to an unsupported declaration type, using an unknown attribute, conflicting attributes, or attributes that are misplaced. This flag can be particularly useful during development to catch and correct instances where attributes are not having their intended effect, potentially leading to suboptimal generated code or unexpected behavior. Meanwhile, -Wno-ignored-attributes suppresses these warnings and is the default behavior, allowing for a cleaner build output especially in cases where the ignored attributes are known and deemed harmless. This might be desired in large code bases where third-party libraries or legacy code introduce attributes that are not relevant to the current compilation target or build configuration. By attentively managing the use of these flags and understanding when attributes are being ignored, developers can ensure that their code is as efficient, portable, and behaviorally correct as possible. Additionally, recognizing the cause of ignored attributes can be a step toward refining code, making it cleaner and more precise in terms of compiler directives and optimizations.

AI Generated

Supergroups

• -Wattributes (85 elements)

Warnings/Remarks

Default Active (Deactivate with -Wno-ignored-attributes)

ext_cannot_use_trivial_abi	warning: 'trivial_abi' cannot be applied to A
warn_alias_to_weak_alias	warning: alias ifunc will always resolve to A even if weak definition of B is overridden
warn_alias_with_section	warning: alias ifunc will not be in section 'A' but in the same section as the aliasee resolver
warn_aligned_attr_underaligned	warning: requested alignment is less than minimum alignment of B for type A
warn_attr_abi_tag_namespace	warning: 'abi_tag' attribute on non-inline anonymous namespace ignored
warn_attribute_after_definition_ignored	warning: attribute A after definition is ignored
warn_attribute_cmse_entry_static	warning: 'cmse_nonsecure_entry' cannot be applied to functions with internal linkage
warn_attribute_dllexport_explicit_instantiation_def	warning: 'dllexport' attribute ignored on explicit instantiation definition
warn_attribute_has_no_effect_on_compile_time_if	warning: attribute A has no effect when annotating an 'if constexpr consteval ' statement
warn_attribute_has_no_effect_on_infinite_loop	warning: attribute A has no effect when annotating an infinite loop
warn_attribute_iboutlet	warning: A attribute can only be applied to instance variables or properties
warn_attribute_ignored	warning: A attribute ignored
warn_attribute_ignored_for_field_of_type	warning: A attribute ignored for field of type B
warn_attribute_ignored_no_calls_in_stmt	warning: A attribute is ignored because there exists no call expression inside the statement
warn_attribute_ignored_non_function_pointer	warning: A attribute is ignored because B is not a function pointer
warn_attribute_ignored_on_inline	warning: A attribute ignored on inline function
warn_attribute_ignored_on_non_definition	warning: A attribute ignored on a non-definition declaration
warn_attribute_invalid_on_definition	warning: 'A' attribute cannot be specified on a definition
warn_attribute_no_decl	warning: attribute A ignored, because it is not attached to a declaration
warn_attribute_nonnull_no_pointers	warning: 'nonnull' attribute applied to function with no pointer arguments
warn_attribute_nonnull_parm_no_args	warning: 'nonnull' attribute when used on parameters takes no arguments
warn_attribute_not_on_decl	warning: A attribute ignored when parsing type
warn_attribute_pointer_or_reference_only	warning: A attribute only applies to a pointer or reference (B is invalid)
warn_attribute_pointers_only	warning: A attribute only applies to   constant pointer arguments
warn_attribute_precede_definition	warning: attribute declaration must precede definition
warn_attribute_return_pointers_only	warning: A attribute only applies to return values that are pointers
warn_attribute_return_pointers_refs_only	warning: A attribute only applies to return values that are pointers or references
warn_attribute_sentinel_named_arguments	warning: 'sentinel' attribute requires named arguments
warn_attribute_sentinel_not_variadic	warning: 'sentinel' attribute only supported for variadic functions blocks
warn_attribute_type_not_supported	warning: A attribute argument not supported: B
warn_attribute_type_not_supported_global	warning: A attribute argument 'B' not supported on a global variable
warn_attribute_unknown_visibility	warning: unknown visibility A
warn_attribute_void_function_method	warning: attribute A cannot be applied to functions Objective-C method without return value
warn_attribute_weak_on_field	warning: __weak attribute cannot be specified on a field declaration
warn_attribute_weak_on_local	warning: __weak attribute cannot be specified on an automatic variable when ARC is not enabled
warn_attribute_wrong_decl_type	warning: A attribute   only applies to functions unions variables and functions functions and methods functions, methods and blocks functions, methods, and parameters variables variables and fields variables, data members and tag types types and namespaces variables, functions and classes kernel functions non-K&R-style functions
warn_attribute_wrong_decl_type_str	warning: A attribute   only applies to C
warn_attributes_likelihood_ifstmt_conflict	warning: conflicting attributes A are ignored
warn_block_literal_attributes_on_omitted_return_type	warning: attribute A ignored, because it cannot be applied to omitted return type
warn_cconv_unsupported	warning: A calling convention is not supported for this target on variadic function on constructor/destructor on builtin function
warn_cxx11_gnu_attribute_on_type	warning: attribute A ignored, because it cannot be applied to a type
warn_declspec_allocator_nonpointer	warning: ignoring __declspec(allocator) because the function return type A is not a pointer or reference type
warn_declspec_attribute_ignored	warning: attribute A is ignored, place it after " class struct interface union enum enum class enum struct " to apply attribute to type declaration
warn_deprecated_anonymous_namespace	warning: 'deprecated' attribute on anonymous namespace ignored
warn_deprecated_ignored_on_using	warning: A currently has no effect on a using declaration
warn_dllimport_dropped_from_inline_function	warning: A redeclared inline; B attribute ignored
warn_duplicate_attribute	warning: attribute A is already applied with different arguments
warn_duplicate_attribute_exact	warning: attribute A is already applied
warn_function_attribute_ignored_in_stmt	warning: attribute is ignored on this statement as it only applies to functions; use 'A' on statements
warn_function_stmt_attribute_precedence	warning: statement attribute A has higher precedence than function attribute ' always_inline flatten noinline '
warn_gc_attribute_weak_on_local	warning: Objective-C GC does not allow weak variables on the stack
warn_gnu_inline_attribute_requires_inline	warning: 'gnu_inline' attribute requires function to be marked 'inline', attribute ignored
warn_ignored_ms_inheritance	warning: inheritance model ignored on primary template partial specialization
warn_ignored_objc_externally_retained	warning: 'objc_externally_retained' can only be applied to local variables of retainable type with strong ownership
warn_import_on_definition	warning: import module name cannot be applied to a function with a definition
warn_internal_linkage_local_storage	warning: 'internal_linkage' attribute on a non-static local variable is ignored
warn_interrupt_attribute_invalid	warning: MIPS MSP430 RISC-V 'interrupt' attribute only applies to functions that have no parameters a 'void' return type
warn_microsoft_qualifiers_ignored	warning: qualifiers after comma in declarator list are ignored
warn_mig_server_routine_does_not_return_kern_return_t	warning: 'mig_server_routine' attribute only applies to routines that return a kern_return_t
warn_mismatched_import	warning: import module name (B) does not match the import module name (C) of the previous declaration
warn_mmap_unknown_attribute	warning: unknown attribute 'A'
warn_nocf_check_attribute_ignored	warning: 'nocf_check' attribute ignored; use -fcf-protection to enable the attribute
warn_noderef_on_non_pointer_or_array	warning: 'noderef' can only be used on an array or pointer type
warn_nothrow_attribute_ignored	warning: 'nothrow' attribute conflicts with exception specification; attribute ignored
warn_ns_attribute_wrong_parameter_type	warning: A attribute only applies to Objective-C object pointer pointer-to-CF-pointer pointer/reference-to-OSObject-pointer parameters
warn_ns_attribute_wrong_return_type	warning: A attribute only applies to functions methods properties that return an Objective-C object a pointer a non-retainable pointer
warn_objc_direct_ignored	warning: A attribute isn't implemented by this Objective-C runtime
warn_objc_direct_property_ignored	warning: direct attribute on property A ignored (not implemented by this Objective-C runtime)
warn_opencl_attr_deprecated_ignored	warning: A attribute is deprecated and ignored in B
warn_require_const_init_added_too_late	warning: 'require_constant_initialization' attribute added after initialization of variable
warn_riscv_repeated_interrupt_attribute	warning: repeated RISC-V 'interrupt' attribute
warn_sycl_kernel_invalid_template_param_type	warning: template parameter of a function template with the 'sycl_kernel' attribute cannot be a non-type template parameter
warn_sycl_kernel_num_of_function_params	warning: function template with 'sycl_kernel' attribute must have a single parameter
warn_sycl_kernel_num_of_template_params	warning: 'sycl_kernel' attribute only applies to a function template with at least two template parameters
warn_sycl_kernel_return_type	warning: function template with 'sycl_kernel' attribute must have a 'void' return type
warn_transparent_union_attribute_field_size_align	warning: alignment size of field B (C bits) does not match the alignment size of the first field in transparent union; transparent_union attribute ignored
warn_transparent_union_attribute_floating	warning: first field of a transparent union cannot have floating point vector type B; transparent_union attribute ignored
warn_transparent_union_attribute_not_definition	warning: transparent_union attribute can only be applied to a union definition; attribute ignored
warn_transparent_union_attribute_zero_fields	warning: transparent union definition must contain at least one field; transparent_union attribute ignored
warn_type_attribute_wrong_type	warning: 'A' only applies to function pointer Objective-C object or block pointer types; type here is C
warn_unhandled_ms_attribute_ignored	warning: __declspec attribute A is not supported
warn_unsupported_target_attribute	warning: unsupported duplicate unknown   CPU tune CPU 'C' in the ' target target_clones target_version ' attribute string; ' target target_clones target_version ' attribute ignored
warn_unused_result_typedef_unsupported_spelling	warning: '[[ nodiscard gnu::warn_unused_result ]]' attribute ignored when applied to a typedef; consider using '__attribute__((warn_unused_result))' or '[[clang::warn_unused_result]]' instead
warn_wrong_clang_attr_namespace	warning: '__clang__' is a predefined macro name, not an attribute scope specifier; did you mean '_Clang' instead?

Default Inactive (Activate with -Wignored-attributes)

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